The present invention relates to an electronic fuel injection control device for an internal combustion engine and method thereof in particular suitable for engine start control wherein a start time of the internal combustion engine which represents the air/fuel ratio during the engine start is detected and the detected start time is used for determining the amount of fuel to be injected in the next engine start for realizing an adaptive control.
The amount of fuel to be injected during start of the internal combustion engine in a conventional electronic fuel injection control device was determined by outputting a pulse having a fixed pulse width to fuel injectiors which is obtained without regarding the amount of air taken in the cylinders. Therefore the pulse having a fixed pulse width was corrected by assuming the intake air into the cylinders with the engine water temperature and engine rotating number and had to be set at a value which enabled engine start at all conditions.
In such conventional electronic fuel injection control device for an internal combustion engine, no influences with regard to scattering or non-uniformity of such as fuel injector and engine performance and difference of fuel nature such as heavy gasoline and light gasoline were taken into consideration such that air/fuel ratio during engine start scattered due to the above factors and there arised a problem that the start characteristics of internal combustion engine differed in every vehicle and every region where the vehicles were used.
JP-B-63-21816 (1988) discloses one solution of the above problem wherein it is experimentally proved that air/fuel ratio during engine start has a predetermined correlation with a time T.sub.1 until initial explosion and a time T.sub.2 from the initial explosion to a complete explosion which determines engine start time and at engine start a stored fuel correction value during engine start corresponding to a detected engine water temperature is retrieved and used for the engine start and time T.sub.1 and time T.sub.2 are also detected and these values are compared with the previous values for the same engine water temperature and the fuel correction value during engine start used for the present engine start is modified based upon the comparison result with reference to the proved correlation and is stored for the next engine start at the corresponding engine water temperature.
However, according to an experiment of the present inventor, with the control device indicated above, the engine start time scatters about 0.3 sec even in an optimum air/fuel ratio and when in a lean air/fuel ratio the scattering further increases. Still further, in the above control device when the time T.sub.1 until initial explosion is long and the time T.sub.2 until complete explosion is short, the air/fuel ratio during engine start is judged lean. However when fuel remains within the intake tube due to such as fuel leakage from the fuel injector the air/fuel ratio during engine start is rendered excess rich such that the initial explosion is never caused before the remaining fuel component is scavenged and approaches to a combustible air/fuel ratio. This indicates that there is an instance that the time T.sub.1 until intial explosion is long and the time T.sub.2 until complete explosion is short even if the air/fuel ratio during engine start is rich such that the above control device may erroneously determine air/fuel ratio during engine start.
The engine start time greatly varies depending upon the water temperature at engine start, because viscosity of the engine oil and the battery voltage are affected by the water temperature at engine start, for this reasons in the above control device great many sets of the time T.sub.1, time T.sub.2 and fuel correction value during engine start corresponding to respective water temperatures at engine start have to be stored in a RAM which necessitates increase of memory capacity in the control device.